The neuronal ceroid lipofuscinoses (NCLs) are progressive, fatal neurodegenerative lysosomal storage disorders that collectively represent the most common inherited neurodegenerative storage disorder of childhood with an incidence of up to 1 in 12,500 five births. There is currently little known regarding which neuronal populations are affected in the NCLs and how their normal structure is compromised. These data can be obtained by systematically analyzing the cellular components of the affected CNS and looking for common themes by comparing tissue from patients to newly developed mouse models of NCL. The main goals of this project are to define the extent and progression of pathological changes in juvenile NCL (JNCL), the most prevalent form of the disorder. This information is currently lacking, but is absolutely essential for understanding disease processes and effectively targeting and evaluating the efficacy of novel therapeutic approaches. We shall use unbiased stereological methodology to characterize at a regional, perikaryal, dendritic and synaptic level the extent of neuropathological changes in murine and human JNCL tissue. We will accomplish our goals with the following specific aims: 1) To quantify changes in the volume and gross cellular organization of the hippocampus, cerebellum and cortical sub-regions; 2) To examine neuronal soma in these regions in more detail to define the extent and timing of changes in the number and volume of i) the total neuronal population and ii) GABAergic interneurons, a neuronal sub population which our preliminary evidence indicates are significantly affected in this disorder, and. iii) extend this analysis to neuronal populations that share common phenotypic characteristics; 3) To define pathologic changes in the dendritic arbor and synaptic contacts made by these neurons; 4) To determine the extent of glial activation and kfiammatory responses in JNCL and their timing in relation to pathological changes in neurons. The information gained from these comparative studies will a) further validate the clinical relevance of these animal models to test potential therapies; b) permit more efficient targeting of treatment strategies to appropriate neuronal populations; c) potentially reveal novel populations of affected neurons; and d) establish a series of pathological landmarks essential for evaluating therapeutic efficacy.